2013/2/8 Vincent Guittot <[email protected]>:
> On 8 February 2013 16:35, Frederic Weisbecker <[email protected]> wrote:
>> What if the following happen (inventing function names but you get the idea):
>>
>> CPU 0 CPU 1
>>
>> dom = new_domain(...) {
>> nr_cpus_busy = 0;
>> set_idle(CPU 1); old_dom =get_dom()
>> clear_idle(CPU 1)
>> }
>> rcu_assign_pointer(cpu1_dom, dom);
>>
>>
>> Can this scenario happen?
>
> This scenario will be:
>
> CPU 0 CPU 1
>
> detach_and_destroy_domain {
> rcu_assign_pointer(cpu1_dom, NULL);
> }
>
> dom = new_domain(...) {
> nr_cpus_busy = 0;
> set_idle(CPU 1); old_dom =get_dom()
> old_dom is null
> //clear_idle(CPU
> 1) can't happen because a null domain is attached so we will never
> call nohz_kick_needed which is the only place where we can clear_idle
> }
> rcu_assign_pointer(cpu1_dom, dom);
So is the following possible?
= CPU 0 = = CPU 1=
detach_and_destroy_domain {
rcu_assign_pointer(cpu1_dom, NULL);
}
dom = new_domain(...) {
nr_cpus_busy = 0;
set_idle(CPU 1);
}
clear_idle(CPU 1)
dom = rcu_dereference(cpu1_dom)
//dom == NULL, return
rcu_assign_pointer(cpu1_dom, NULL);
set_idle(CPU 1)
dom = rcu_dereference(cpu1_dom)
//dec nr_cpus_busy, making it negative
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